BMIs are a worldwide technology in course of development, which make possible the direct triggering of prostheses or technical devices by brain activity of a proband. The basic task of a motor BMI, to predict the intended movement from neuronal activity, classically is tried to be resolved by gauging a prevision model in a learning phase and following application of the prevision model on a virtual or real movement in an operational phase.
However, the basic supposition of this strategy is actually violated, i.e. that the neuronal activity would be stationary between training and operational phase or within the operational phase. On the contrary, the neuronal activity is dynamic even on relatively small time scales. Non-concluding reasons for this can be the plasticity of the brain (new interconnections, experience, ageing, . . . ), the cognitive state (attention, motivation, tiredness, time of day, change due to parallel activity, . . . ), differences between training and operating scenario (imagined compared to executed movement) or variability of derivation (small movements of the electrodes, change of the dielectricity of the gel (by hardening), with the help of which EEG-electrodes are applied, death of neurons in the case of single cell derivation, . . . ).
A precise and long-term stable prevision for reconstruction of conscious thoughts from the (in practice electric) brain signals in a BMI should be able to deal with these dynamics.
For the practical implementation of the derivation of the neuronal activity, a flexible foil is used that is tightly packed with miniature electrode contacts, implanted on the surface of selected areas of the cerebral cortex. The electric fields measured between the electrodes, resulting from the activity of groups of neurons (neuronal population activity), are fed into a multi-channel amplifier. The amplifier processes the neuronal signals of the single electrodes with high temporal resolution and delivers them in real time to a computerized system for signal processing. This system calculates from the nerve signals the action intention of the patient for certain trained voluntary movements that the patient can no longer execute himself. The calculated movement intention is then converted into a command signal, for example for an arm prosthetis or a computer cursor.